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Orthodox Wisdom Says to Restrict This as Your Pet Ages — Study Says Don’t

Retired veterinary nutritionist proved that even in animals with kidney failure, restricting this failed to improve health or longevity. In fact, the more it was restricted, the sicker these animals became. But here's the new caveat that keeps getting ignored.

feeding senior cats


  • If you have a senior cat in the family, it’s important to routinely re-evaluate her diet to ensure you’re meeting the dynamically changing needs of her aging body
  • Out: Feeding older cats reduced protein diets. In: Feeding older cats a moisture-rich diet loaded with high-quality protein. Research shows cats actually need more protein as they age, not less
  • The quality, digestibility and biologic value of the protein in your cat’s diet is extremely important
  • The best food for cats of all ages is a nutritionally balanced, species-appropriate fresh food diet

Editor's Note: This article is a reprint. It was originally published February 13, 2018.

If you have a senior cat in the family, you're in good company, as millions of households in the U.S. have at least one kitty over the age of 7. But unlike humans and many dog breeds, it's not always easy to tell a cat's age just by looking at her.

Cats mature quickly during their first few years of life, and then things level off. The method many experts use to calculate a cat's age in human years is to add 15 years for the first year of life, 10 years for the second year of life and four years for every year after that. So, for example:

  • A 4-year-old cat is 33 in human years [15 + 10 + 4 + 4]
  • An 8-year-old cat is 49 [15 + 10 + (4x6)]
  • A 15-year-old cat is 77 [15 + 10 + (4x13)]

It's important to keep track of your cat's age for many reasons, one of the most important of which is so you can ensure you're feeding her the best nutrition for the dynamically changing needs of her body as she as she ages.

For many years, the veterinary community believed cats required reduced protein diets as they aged. This is because many older cats, having spent a lifetime eating processed pet food made with difficult-to-digest, poor-quality rendered protein, have compromised kidney and liver function. If you insist on feeding your cat feed-grade protein, you should probably reduce the amount in her diet as she ages to reduce wear and tear on her vital organs negatively impacted by poor-quality foods.

The chronic stress created by a diet that is hard to digest and assimilate causes premature aging and dysfunction in the organs of digestion and detoxification. However, reduced protein cat food can be a recipe for disaster, because we now know aging cats actually need more protein than their younger counterparts.

Back in the 1990s, retired veterinary nutritionist Dr. Delmar Finco discovered protein requirements actually increase as pets age. He demonstrated that even in animals with kidney failure, restricting protein didn't improve their health or longevity.1

In fact, Finco's research proved cats on low-protein diets develop hypoproteinemia, which is an abnormally low level of protein in the blood. The cats had muscle wasting, became catabolic and lost weight. The more protein was restricted, the sicker these kitties became.

Cats Need High-Quality Animal Protein, and Older Cats Need More

Finco discovered it was the level of phosphorus in foods, not necessarily the amount of protein that exacerbated kidney disease, and thanks to his groundbreaking research, veterinary recommendations have changed. These days, we recommend a diet containing excellent-quality protein that is highly digestible and assimilable for animals struggling with under-functioning kidneys and livers. We also recommend restricting phosphorus in the diet, but not necessarily protein.

If your cat is in the later stages of kidney failure, as defined by the International Renal Interest Society (IRIS), a reduced amount of excellent-quality protein is suggested, but should still be offered in a kidney-friendly fresh food format. We now know that cats, as true carnivores, require lots of high-quality animal protein not only to maintain good organ and immune function, but also to maintain healthy muscle mass as they go through life and the aging process.

The Quality of the Protein You Feed Your Cat Is as Important as the Quantity

The quality of the protein you feed your senior cat is of utmost importance. Highly digestible and assimilable protein, coupled with high moisture content, is the type of nutrition that causes the least amount of stress on your kitty's aging organs.

It's sort of a well-kept secret, especially among processed pet food manufacturers, that protein quality is extremely variable. There are highly assimilable and digestible animal proteins (proteins your kitty's body can easily absorb and make use of), and there are plant proteins that are both biologically inappropriate and difficult to process. There are also animal proteins that are wholly indigestible. For example, animal beaks, feet, hides, tails and snouts are 100% protein, but all 100% is indigestible.

Not All Protein Is Created Equal

All protein has a biologic value, which is its usable amino acid content. Eggs have the highest biologic value at 100%. Fish is a close second at 92%. Feathers, as you might guess, have zero biologic value. They are technically animal protein, but they are neither digestible nor assimilable.

There are also foods that are high in (plant) protein but biologically inappropriate for cats. Soy is a good example, with a biologic value of 67%. Many popular pet foods contain soy as a protein source, as well as corn. This is an inexpensive way for pet food manufacturers to increase protein content on the guaranteed analysis printed on the label. But because soy and corn are not species-appropriate, they don't belong in your cat's diet.

Since digestion and assimilation are not measured for pet foods, manufacturers are not penalized for adding protein that has little to no nutritional value for the species of animal eating it.

In addition to corn and soy (as well as other grains) being inflammatory and incomplete proteins for carnivores, there are many other reasons not to feed carbohydrates to cats. Mycotoxins, GMOs, glyphosate exposure and sugar load (which leads to lifestyle-induced diabetes), as well as obesity and arthritis are all solid reasons to avoid offsetting high-quality protein with cheap fillers.

The Best Diet for Your Aging Cat

Some foods are metabolically stressful, while others create low metabolic stress on your cat's body. The nutrition that generates the least amount of metabolic stress for most cats, regardless of age, is whole, raw, unprocessed, organic, non-GMO and in its natural form. This of course includes animal meat, which should be the foundation of your kitty's diet throughout her life.

Foods that have not been highly processed are the most assimilable for a cat's body. These foods are biologically appropriate. All the moisture in the food remains in the food, whereas foods that have been extruded (most dry food) can have drastically depleted moisture content — as low as 12%.

If you can't feed fresh food (raw or gently cooked), the second best diet is a dehydrated or freeze-dried balanced diet that has been reconstituted with plenty of water. Your cat's kidneys and liver can be further stressed as a result of chronic low-grade dehydration, so all foods served dry can pose a problem long term.

If your cat is overweight, no matter her age, it makes sense to reduce calories (control the amount of food you are offering). What does not make sense is adding fiber. Many weight management ("low-fat") and senior cat food formulas contain loads of fiber, which is biologically inappropriate nutrition.

I recommend serving your cat food in its natural state to provide needed moisture, and to ensure the highest level of biologic assimilation and digestion. That means feeding a nutritionally balanced, antioxidant rich, species-appropriate diet that includes omega-3 essential fats, such as krill oil.

Moisture is an aging cat's best friend, so encourage your kitty to drink by offering a variety of glass, metal or food-grade ceramic water bowls around the house or a drinking fountain, in addition to minimizing (or preferably eliminating) dry food. However, if your kitty is addicted to terrible food, adding a whole body supplement, such as Feline Whole Body Support is a good idea. Adding bone broth to a dry food addict's meal is also a great way to increase hydration and fluid balance in your cat.

Sources and References

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